Name: 2d nmr correlation peaks and bond links
Uploaded: 2024-12-05T18:32:27.000Z
Duration: 1 min 18 s
Channel: JoVE

Heteronuclear correlation techniques investigate the coupling between different nuclei&#8212;often a proton and carbon-13 or nitrogen-15.
A typical spectrum displays the X-nucleus chemical shift on one axis and the proton chemical shift on the other, with cross-peaks indicating the proton&#8211;X correlations.
Standard heteronuclear correlation spectroscopy, or HETCOR, enhances X-nucleus signals using polarization and is preferred for high X-axis resolution.
The heteronuclear single-quantum and multiple-quantum correlation techniques&#8212;HSQC and HMQC &#8212;explore proton&#8211;X one-bond correlations.
HSQC generates a spectrum like that of HMQC but uses a different suppression method, resulting in higher X-nucleus peak resolution.
Heteronuclear multiple-bond correlation or HMBC, focuses on longer-range proton&#8211;X connectivity, ignoring direct one-bond correlations.
Gradient HMBC enhances the suppression of interfering signals, making it useful for complex molecules with overlapping signals

2d nmr: overview of heteronuclear correlation techniques

2D NMR: Overview of Heteronuclear Correlation Techniques

Heteronuclear correlation spectroscopy is an analytical technique that investigates the coupling between different types of nuclei, often a proton and an X-nucleus, such as carbon-13 or nitrogen-15. This method is commonly used in nuclear magnetic resonance (NMR) spectroscopy to gain insights into complex chemical compounds&#39; structural and compositional aspects. A typical heteronuclear correlation spectrum displays X-nucleus chemical shifts on one axis and a proton spectrum on the other axis. Cross-peaks reveal the connection between specific protons and X-nuclei.
The main heteronuclear correlation experiments include HETCOR, HSQC, HMQC, and HMBC. HSQC, HMQC, and HMBC record the proton spectrum, whereas the X-nucleus spectrum is recorded by standard heteronuclear correlation spectroscopy or HETCOR. The HETCOR-HMQC-HSQC group of experiments cannot detect X-nuclei without an attached proton. HETCOR is used when ultrahigh peak resolution is required along the X-nucleus axis.
The heteronuclear single quantum correlation technique, or HSQC, investigates proton-to-X-nucleus single bond correlations. In an HSQC experiment, polarization is transferred from a proton nucleus to a neighboring X-nucleus and then back to the proton nucleus. The signal from the proton nuclei is then recorded. HSQC generates a spectrum like that of heteronuclear multiple-quantum correlation spectroscopy or HMQC but uses a different suppression method, providing better X-nucleus resolution along the axis.
Heteronuclear multiple-bond correlation, or HMBC, is a proton-detected experiment, like HMQC but with a longer initial delay time. This experiment is used to observe long-range proton to X-nucleus connectivity separated by 2-3 bonds, with some experiments going out to 4 or 5 bonds. In an HMBC experiment, direct one-bond correlations are suppressed as part of the sequence. The spectra of HMBC give rise to cross peaks that correlate which protons are coupled to what other specific X-nucleus is more than one bond away. The gradient HMBC (gHMBC) pulse sequence offers better suppression of interfering signals, making it particularly useful for analyzing complex molecules with overlapping signals.

Heteronuclear correlation spectroscopy is an analytical technique that investigates the coupling between different types of nuclei, often a proton and an ...

2d-nmr-overview-of-heteronuclear-correlation-techniques

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Analytical Chemistry

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Advanced Nuclear Magnetic Resonance Spectroscopy

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KEY TERMS AND CONCEPTS

2d nmr correlation peaks and bond links

Heteronuclear correlation spectroscopy is a 2D NMR method that links different nuclei, usually a proton and an X-nucleus such as carbon-13 or nitrogen-15. It helps scientists study the structure and composition of complex chemical compounds. In a heteronuclear correlation spectrum, one axis shows X-nucleus chemical shifts and the other axis shows the proton spectrum. Cross-peaks mark which protons are connected to which X-nuclei.

The main heteronuclear correlation experiments are HETCOR, HSQC, HMQC, and HMBC. HSQC, HMQC, and HMBC record the proton spectrum, while standard heteronuclear correlation spectroscopy, also called HETCOR, records the X-nucleus spectrum. The HETCOR-HMQC-HSQC group cannot detect X-nuclei that do not have an attached proton. HETCOR is useful when ultrahigh peak resolution is needed along the X-nucleus axis.

HSQC stands for heteronuclear single quantum correlation. It looks at one-bond, or single bond, correlations between a proton and a nearby X-nucleus. In this experiment, polarization moves from the proton to the neighboring X-nucleus and then back to the proton, and the proton signal is recorded. HSQC gives a spectrum like HMQC, but it uses a different suppression method and gives better X-nucleus resolution along the axis.

HMBC stands for heteronuclear multiple-bond correlation. It is a proton-detected experiment like HMQC, but it uses a longer initial delay time. HMBC is used to see longer-range proton to X-nucleus connections that are separated by 2 to 3 bonds, and some experiments extend to 4 or 5 bonds. Direct one-bond correlations are suppressed in the sequence, so the cross-peaks show which protons are coupled to X-nuclei farther away. The gradient HMBC, or gHMBC, pulse sequence gives better suppression of interfering signals and is helpful for complex molecules with overlapping signals.

2D NMR Correlation Peaks and Bond Links

&sup1;h nmr of conformationally flexible molecules: temporal resolution

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¹H NMR Ring Flips and Signal Averaging

¹H NMR can show how fast molecular motion changes the signals we see. In cyclohexane, the chair form flips rapidly between two equivalent chair conformers at room temperature. This happens about 10^5 times per second, and the two shapes stay in equilibrium. During ring flipping, an axial proton becomes equatorial, and an equatorial proton becomes axial. These changes are too fast to detect on the NMR timescale. As a result, the NMR spectrometer cannot tell the axial and equatorial protons...

&sup1;h nmr of conformationally flexible molecules: variable-temperature nmr

h-nmr-of-conformationally-flexible-molecules-variable-temperature-nmr

Cyclohexane Ring Flipping in Variable-Temperature NMR

Cyclohexane ring flipping can be tracked with variable-temperature NMR. The experiment helps distinguish the axial and equatorial protons in a deuterium-substituted cyclohexane sample. Deuterium is used to replace eleven of the twelve protons. This reduces possible peak splitting from spin-spin coupling between neighboring protons. The remaining proton shifts between the axial and equatorial positions as the chair form of cyclohexane changes. At room temperature, ring flipping is very fast, so...

&sup1;h nmr of labile protons: temporal resolution

h-nmr-of-labile-protons-temporal-resolution

OH Proton Exchange in Ethanol NMR

The OH proton in alcohols can shift and split differently in a proton NMR spectrum. Its position usually falls around 2 to 5 ppm, but the exact value depends on the alcohol and the sample conditions. This proton is labile, which means it can exchange rapidly with other molecules. Hydrogen bonding to oxygen or nitrogen changes the electron density around the proton. That change affects the chemical shift seen in the proton NMR spectrum. The exchange rate also affects spin-spin coupling between...

&sup1;h nmr of labile protons:  deuterium (&sup2;h) substitution

h-nmr-of-labile-protons-deuterium-h-substitution

Using D2O to Identify OH Protons

Deuterium substitution can help identify labile protons in ¹H NMR spectra. Labile protons are hydrogens that can be replaced by another hydrogen isotope. In this lesson, deuterium is used to simplify the spectrum of ethanol. Deuterium, or ²H, is one of the three isotopes of hydrogen. Its nucleus contains one proton and one neutron. When D₂O is added to a pure dry ethanol solution, the labile proton on the –OH group is replaced by deuterium. A proton NMR spectrum does not show signals from...

nuclear overhauser enhancement (noe)

Using NOE to Map Nearby Nuclei

Nuclear Overhauser enhancement, or NOE, shows how irradiation of one spin-active nucleus can change the signal of nearby nuclei. These nuclei do not have to be chemically bonded or connected through J-coupling. The effect comes from through-space interactions between nuclear spins. NOE gets weaker as the distance between nuclei increases. It is generally not observed beyond about 4 angstroms. Dipole-dipole interactions between neighboring spin-active nuclei transfer nuclear spin polarization,...

insensitive nuclei enhanced by polarization transfer (inept)

insensitive-nuclei-enhanced-by-polarization-transfer-inept

NMR Signal Boosting with INEPT Pulses

INEPT is an NMR method that boosts weak signals from low-abundance nuclei. It is used to detect nuclei such as carbon-13 and nitrogen-15 in small molecules. The goal is to make these hard-to-see nuclei easier to observe in an NMR spectrum. The technique works by transferring polarization from a more abundant nucleus, usually hydrogen-1, to the nucleus of interest. Hydrogen-1 has higher receptivity, so it can provide the starting signal boost. Spin coupling then helps move that polarization to...

double resonance techniques: overview

Spin Decoupling in NMR Spectroscopy

Spin decoupling is a key use of double resonance in nuclear magnetic resonance (NMR) spectroscopy. It uses two radiofrequency pulses or frequencies at the same time to act on two different nuclear spins. This makes the spectrum simpler and easier to read. In spin decoupling, one type of nucleus is selectively suppressed while the signal from another nucleus is observed. The radiofrequency pulse sequence removes the coupling with one nuclide and can greatly improve resolution. As a result, the...

two-dimensional (2d) nmr: overview

2D NMR Spectra and Signal Mapping

Two-dimensional (2D) NMR helps make sense of crowded NMR data from large and complex molecules, such as natural products. A 1D NMR spectrum can have overlapping signals and complicated splitting patterns. 2D NMR adds a second frequency axis, which helps show the coupling information between nucleus A and nucleus B in a molecule. 2D spectra are built in four steps. First is the preparation period, when nucleus A is excited with a radiofrequency pulse. Next is the evolution, or wait, period t1.

2d nmr: overview of homonuclear correlation techniques

2d-nmr-overview-of-homonuclear-correlation-techniques

2D NMR Correlation Paths in Molecules

2D NMR homonuclear correlation techniques show how nuclei of the same type connect within a molecule. In nuclear magnetic resonance (NMR) spectroscopy, these methods reveal scalar couplings, which are interactions between nearby nuclei through bonds. That information helps identify which atoms are linked and how a molecule is put together. COSY is the main homonuclear correlation experiment. COSY90 is the standard 2D COSY method and uses a second 90-degree pulse to improve sensitivity and...

2d nmr: homonuclear correlation spectroscopy (cosy)

2d-nmr-homonuclear-correlation-spectroscopy-cosy

Reading Proton Coupling with COSY Maps

COSY is a 2-dimensional NMR method that shows which protons are coupled to each other. It is used to spot geminal and vicinal coupling in a sample. This makes it helpful for reading proton relationships in complex spectra. The ethyl acetate example shows how COSY is built from the 1D proton NMR spectrum. The same chemical shift scale appears on both the vertical and horizontal axes. The peaks along the diagonal are called diagonal peaks, and they match the three peaks seen in the 1D proton...

Heteronuclear correlation spectroscopy is a 2D NMR method that links different nuclei, usually a proton and an X-nucleus such as carbon-13 or nitrogen-15. It helps scientists study the structure and composition of complex chemical compounds. In a heteronuclear correlation spectrum, one axis shows X-nucleus chemical shifts and the other axis shows the proton spectrum. Cross-peaks mark which protons are connected to which X-nuclei. The main heteronuclear correlation experiments are HETCOR, HSQC,...

2d nmr: heteronuclear single-quantum correlation spectroscopy (hsqc)

2d-nmr-heteronuclear-single-quantum-correlation-spectroscopy-hsqc

HSQC NMR Maps Carbon-Proton Connections

HSQC NMR maps the direct links between hydrogen atoms and the carbons they are attached to. It is a 2D NMR method, so it shows the data on two axes instead of one. The experiment is similar to heteronuclear correlation spectroscopy, or HETCOR, but HSQC is more sensitive. In an HSQC spectrum, the proton chemical shift appears on the horizontal F2 axis. The 13C chemical shift appears on the vertical F1 axis. The spectrum also includes the matching proton and 13C spectra. The contour plot does...

key terms and concepts

Learn how heteronuclear correlation, HSQC, HMQC, HETCOR, and HMBC reveal bond links in 2D NMR spectra using proton and X-nucleus cross-peaks.

2D NMR Correlation Peaks and Bond Links | JoVE K12

analytical chemistry

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2D NMR Correlation Peaks and Bond Links

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